1. Field of the Invention
This invention relates generally to drill stem testing tools, and particularly to a new and improved full bore sampler and safety valve apparatus for trapping a flowing sample of formation fluids that may be produced from an isolated well interval.
2. Background Art
A drill stem test may be considered to be a temporary completion of an earth formation that has been intersected by a well bore. A packer is run into the well on a pipe string and is set to isolate the interval of the well bore to be tested, and then a test valve is opened to permit fluids in the formation to flow into the bore hole and up into the pipe string to obtain an indication of the commercial potential of the well. Pressure data is recorded with the test interval open and then shut in, from which many useful parameters such as permeability and initial reservoir pressure can be determined. It also is desirable to collect an actual sample of the fluids for subsequent laboratory analysis.
A sampler that has been used for many years with great success is disclosed in Nutter U.S. Pat. No. 3,308,887, assigned to the assignee of this invention. As shown in FIG. 3B of this patent, the flow of formation fluid is routed through an annular chamber having sleeve valves at each end that simultaneously can be opened and closed. When the valves finally are closed at the end of the test, a flowing sample of the fluid being produced is entrapped at formation conditions of temperature and pressure. However, the testing apparatus shown in the Nutter patent has a barrier that blocks vertical access through the tool and which must be removed before other equipment such as a pressure recorder or a perforator can be run into the well.
A sampler valve that uses a pair of vertically spaced ball valves to simultaneously open and close the respective ends of a sample chamber is shown in U.S. Pat. No. 4,063,593. The device shown in this patent, while being full-bore, has a number of disadvantages. The ball valve elements move vertically within the housing during operation and are subject to cocking and high friction during movement from open to closed positions. These factors can cause less than adequate operation through improper sealing and closure. Moreover this system is not considered to be particularly sturdy and rugged in construction, which is a highly desirable feature in this type of equipment.
A ball valve of known construction utilizes a rotary actuator system of inner and outer threaded sleeves that are coupled to a ball valve element by push rods. Rotation of one sleeve relative to the other causes axial displacement of the sleeves and movement of the ball valve element between its open and closed positions. The requirement of rotary motion makes this system not particularly applicable to drill stem testing tools where movement of the drill stem during the testing operation should be avoided.